For evaluating and examining various kinds of optical elements and optical parts (hereinafter referred to collectively as optical members) such as optical fibers, various kinds of devices and photonic crystals for use in optical fiber communication which has been coming into wide use in recent years, chromatic dispersion in the optical member is measured.
For evaluation of chromatic dispersion, there have been methods described below. First, there is a method using a time-domain interferometer. In this method an interference waveform on a time-domain is measured using the time-domain interferometer, and the interference waveform is subjected to Fourier transformation, whereby the intensity and phase of a transmission spectrum or reflection spectrum of a measurement object are determined to obtain chromatic dispersion (see Non-Patent Document 1). For this purpose, in order to obtain an interference waveform on the time-domain, an optical delay stage placed in one path of the interferometer is swept back and forth with respect to an optical path, and the intensity of light emitted from the interferometer is measured as a function of delay time obtained from the sweep.
As another method for evaluating chromatic dispersion, a method of measuring an interference waveform on a spectrum axis using a spectrum interferometer is carried out (see Non-Patent Document 2). In this method, light emitted from the interferometer is spectrally resolved through a diffraction grating or spectrometer, interference fringes are measured as a function of a wavelength or frequency, and waveform dispersion is determined from dependency of a spectral phase on the wavelength (or frequency).
Another method is one in which using phase-modulated light, a phase shift associated with optical fiber propagation is directly measured by an electronic measuring instrument such as a network analyzer to determine chromatic dispersion (see Patent Document 1). In addition, there is a method for determining chromatic dispersion using a mode-locked pulse light source (see Patent Document 2). In this method, attention is focused on a specific longitudinal mode, and the phase delay of the longitudinal mode is measured to determine chromatic dispersion.
For detecting a chemical reaction, a biological reaction, an effect of hyperthermia and the like, heat generation associated with the reactions and effect of hyperthermia may be detected. For this purpose, there has been means for detecting a change in refractive index associated with a change in temperature in addition to thermocouples directly detecting a change in temperature. Methods for evaluating a change in refractive index associated with temperature include a method using a thermal lens effect (Non-Patent Document 3). In this method, monitor light is made to collectively enter a sample, and a change in collecting power by a change in temperature is detected as a change in intensity.
Non-Patent Document 1: Kazunori Naganuma, “Laser Research”, Vol. 23, No. 11, 1995, Laser Society Association, pp. 55-66.
Non-Patent Document 2: A. P. Kovacs et al. “Group-delay measurement on laser mirrors by spectrally resolved white-light interferometry” Optics Letters, April 1995, Vol. 20, No. 7, pp. 788-790.
Patent Document 1: Japanese Patent No. 3278129
Patent Document 2: Japanese Patent Laid-Open No. 7-248276
Non-Patent Document 3: M. Terazima et al. “Photothermal investigation of the triplet state of carbon molecule (C60)” Journal of Physical Chemistry 1991 Vol. 95, pp. 9080-9085